Residential magnetic field measurements in France: Comparison of indoor and outdoor measurements

Residential magnetic field (MF) measurements were performed for the first t ime in a representative sample of French dwellings. Exposure levels were as sessed by two methods: indoor and outdoor measurements. Linear and logistic regression models were used to determine factors associated with the time- weighted average (TWA) home MF. TWA magnetic field magnitudes were approxim ately log-normally distributed with geometric means under 0.010 mu T for bo th indoor and outdoor measurements. Only 5% of the dwellings presented indo or MF levels greater than 0.120 mu T (1.2 mG). Both indoor and outdoor MF v ariations were explained by three factors: wiring configuration, the dwelli ng's location (i.e., urban or rural), and housing characteristics (individu al houses or apartment building). The reliability of outdoor spot measureme nts with 30-min bedroom recordings was assessed by an intraclass correlatio n coefficient. The measurements were accurate in rural areas and small town s. In urban centers, local MF variations spoil the outdoor measurement's re liability. If indoor measurements are taken as the reference method, the us e of outdoor instead of indoor measurement leads to an important decrease i n statistical power. Further assessment of MF near high power transmission lines is necessary to evaluate the usefulness of outdoor spot recordings ne ar such lines. The urban MF environment also has to be explored to identify extraneous sources. (C) 1999 Wiley-Liss, Inc.